1. Field of the Invention
The present invention relates generally to flat panel displays, and more particularly to an improvement in resonant driving circuits employing column drivers that maximize energy recovery in the resonant circuit by restricting current flowing through output buffers of the column drivers used to control the column voltage.
2. Description of the Related Art
Electroluminescent displays are advantageous by virtue of their low operating voltage with respect to cathode ray tubes, their superior image quality, wide viewing angle and fast response time over liquid crystal displays, and their superior gray scale capability and thinner profile than plasma display panels. They do have relatively high power consumption, however, due to the inefficiencies of pixel charging, as discussed in greater detail below. This is the case even though the conversion of electrical energy to light within the pixels is relatively efficient. However, the disadvantage of high power consumption associated with electroluminescent displays can be mitigated if the capacitive energy stored in the electroluminescent pixels is efficiently recovered.
U.S. Pat. No. 6,448,950 teaches the combined use of sinusoidal driving and energy recovery from an electroluminescent display panel that has a widely varying capacitance. The resonant energy recovery circuit comprises a primary capacitor connected to the primary winding of a step-down transformer, with the secondary winding of the transformer connected through row or column drivers to the electroluminescent display panel. Separate resonant circuits are employed for rows and columns. The charge discharged from the display panel through the rows is efficiently captured in the primary capacitor and recycled to address the next row to be selected, but the energy discharged through the columns is not as efficiently captured and recycled. The reason for this lower efficiency of energy recovery through the columns has been found to be due to the partial discharge of the panel capacitance through undesirable shunting paths instead of through the energy recovery path to the resonant drive power supply.